1. Field of the Invention
The present invention relates to a video signal compensation apparatus for compensating the video signal inputted to the dot-matrix type display so as to improve display non-uniformity.
2. Description of Prior Art
In conventional video signal compensation apparatuses, a study has been conducted on the display device using a liquid crystal display and the like, and a method of compensation for improving mainly the display characteristics of the liquid crystal panel is specially noted.
For instance, because the input voltage-intensity characteristic of the liquid crystal panel has a non-linear characteristic, when the video signal is directly inputted to the liquid crystal panel, a half-tone display non-uniformity occurs. Accordingly, by providing a look-up-table memory provided with an input/output characteristic which is in a reverse relationship with the input voltage-light transmission characteristic and referring to the memory data thereof, the video signal is converted to carry out compensation of the display non-uniformity. The compensation processings are to be carried out independently by the video signals R, G and B, respectively (e.g. see Japanese Patent Publication KOKAI (Unexamined) No. 62-209478).
With the conventional video signal compensation apparatus of the above type, it is difficult to compensate for the display non-uniformity by the screen position resulting from the recent enlargement in the size of the liquid crystal display. For instance, as the above display non-uniformity, the single panel color filter type display includes the following drawbacks:
(1) Due to the irregularity of liquid crystal elements, the video signal level - screen brightness characteristics at the panel position show differences and non-uniformity occurs in displaying half-tones.
(2) Due to the characteristics such as leakage, even in driving with the same signal, the transmitted light amounts differ between the field starting line and the field ending line, and inclination occurs in the screen brightness distribution.
(3) Owing to the non-uniformity of brightness of the back light (faulty arrangement of fluorescent tube, faulty diffusion of diffusion plate, etc.), the screen brightness become non-uniform.
In the projection display, the following additional drawback is observed:
(4) Owing to the displacement of the optical axis in projecting three colors, non-uniformities of brightness and color occur.
Because of the combination of various display non-uniformities on the screen, the display non-uniformity characteristics at the individual screen positions differ from one another. Accordingly, it has not been possible to perform compensations effective for the whole screen by compensating the video signal by using a look-up-table which has stored only 1 table of data for the whole screen.